1. Field of the Invention
The present invention relates to a polyisocyanurate foam having low smoke-generation, low friability and not bursting (i.e. not scattering as a powder when touched to a flame) and excellent heat-resistance and flame-retardance.
2. Description of the Prior Arts
Polyisocyanurate foams have been prepared by blending and stirring an organic polyisocyanate, and isocyanate-trimerization catalyst and a blowing agent and if necessary, a surfactant. Such foams have excellent heat-resistance and flame-retardance which are resulted by isocyanurate linkages, but have disadvantages in friability, and bursting when touched to a flame and a dense smoke-generation when initially touched to a flame.
In order to improve these disadvantages, various processes for preparing modified polyisocyanurate foams have been proposed, for example, a method of using a polyether as a modifier (U.S. Pat. No. 3,516,950); a method of using a polyester as a modifier (U.S. Pat. No. 3,931,065); a method of introducing polyoxazolidone linkage (U.S. Pat. No. 3,793,236); a method of combined use of a polyether polyol having a molecular weight of higher than 200 and a diol having a molecular weight of lower than 200 as a modifier etc.
These modified polyisocyanurate foams have improved friability and bursting property which are imparted by the modification but still have the disadvantages of decreased flame-resistance and flame-retardance and high smoke-generation. No process for preparing a polyisocyanurate foam which simultaneously posesses the four characteristics of low-smoke generation, low friability, high flame-resistance and high flame-retardance has yet been proposed.
The inventors have studied a process for preparing a polyisocyanurate foam having said four characteristics. As the results, the smoke-generation which has not been overcome could be decreased and the bursting property could be eliminated by trimerizing and foaming an organic polyisocyanate in the presence of an organosilicate such as alkoxysilane. However, the friability of the foam is relatively high to cause certain trouble in the transportation Ashida et al., U.S. Pat. No. 4,072,636.